1. Field of the Invention
The present invention relates to a method for calibrating the deviation of opto-electronic property and apparatus thereof. More particularly, the present invention relates to a method for calibrating deviation in the opto-electronic property of an imaging device and apparatus thereof.
2. Description of the Related Art
In recent years, the computation power of computers increases at a rapid pace and digital media has become one of the major instruments for expressing creativity and imagination. With the development of imaging products based on opto-electronic sensing and related principles, images of various types can be recorded and stored in digital format. There are a number of different digital imaging products including thin film transistor liquid crystal displays (TFT-LCD), digital still cameras, digital video camcorders, scanners and printers, to name a few. In general, the ultimate quality of the output images depends on the front-end image-capturing devices, the digital image processor and the back-end digital image output devices.
After a digital image has been digitally processed, the image is output from the back-end equipment of the digital imaging apparatus as an image display or a document output. Digital image processing (DIP) is a process of using a computer to process two or three-dimensional images. First, an analogue image is ‘digitized’ (that is, converting analogue data into digital ‘0’ and ‘1’ data). The method includes ‘sampling’ the image on all locations and then analyzing and recording the brightness, color and location of each point. Each sampling point of the image is called a pixel and the image is constructed from a set of pixels. Furthermore, the image data related to each pixel including its location, color and brightness are stored as data arrays inside the computer ready for processing.
The aforementioned digital data will pass through the front-end image data input device, the digital image process (DIP) and the back-end image data output device. The DIP uses, for example, various types of image-processing software to perform all kinds of local or whole image processing tasks such as color addition/subtraction, brightness or chromatic adjustment, or deformation or image enlargement/reduction. After the computer has performed arithmetic or logic computations on each element in the data array, the results are displayed on a color display screen. That is, the conventional method uses a software-based (S/W-based) approach for controlling the quality of image, with the image data undergoing sophisticated color reproduction computations using color property files (the files containing the color data standard set by the International Color Consortium (ICC)). In other words, the conventional method provides very little consideration regarding the properties of apparatus or the hardware (H/W-based).
In addition, the front-end image data input device will perform an image-capturing process to obtain the required image data. Similarly, the back-end image data output device will display an image according to the digital data. However, the input and the output of the image data are closely related to the response characteristic of the apparatus or hardware. In other words, both the original image data obtained from the front-end image data input device and the back-end image output device for outputting image are equally critical to the image quality. Therefore, the front-end image data input device and the back-end image output device may affect the image through their intrinsic hardware properties. One major factor affecting the image is the so-called opto-electronic conversion functions (OECFs) or opto-electronic properties for short. Conventionally, for imaging apparatus such as liquid crystal displays, digital cameras or scanners, image properties are adjusted by software registered values after the ultimate output is obtained from the chip or liquid crystal. For example, the image properties are adjusted according to a look-up table (LUT) represented by a matrix.
In the following, an actual example of a common opto-electronic conversion is illustrated. FIG. 1 is a perspective view showing the panel structure of a thin film transistor liquid crystal display (TFT-LCD). As shown in FIG. 1, the thin film transistor (TFT) serves as an electronic switch for controlling video signals and the liquid crystal plays the role of optical switches for the transmission of light from the back-light module to the eyes of a human. In the path of propagation of light, the opto-electronic conversion is based on the opto-electronic properties of the liquid crystal. For example, the liquid crystal molecules will rotate according to a specified voltage and hence has a particular light transmittance. FIG. 2 is a graph showing the opto-electronic curves of liquid crystal molecules under fringe field switching (FFS) mode, in-plane switching (IPS) mode and twisted nematic (TN) mode (the opto-electronic curves of transmittance versus voltage).
Similarly, each image-capturing device such as the digital still camera and the digital video camcorders has a complementary metal oxide silicon (CMOS) image-sensing module. FIG. 3 is a schematic diagram of a pixel array of CMOS image sensors (only a single CMOS image sensor is shown). As shown in FIG. 3, the operating principle of each CMOS image sensor includes absorbing the light from an incident light beam through a photodiode and converting the light energy into an electronic signal to obtain an image data. FIG. 4 is a graph showing the brightness versus voltage opto-electronic characteristic curves of a CMOS image-sensing pixel array corresponding to the three primary colors (red, green and blue).
However, for the image display device or the image capturing device inside an imaging apparatus such as the display panel (for example, a liquid crystal display) or the sensor module (for example, a charge-coupled device image sensor or a complementary metal oxide semiconductor image sensor), any deviation in opto-electronic characteristic of the hardware is not rectified. In a word, the effect of the opto-electronic characteristic of the hardware on the output image is often neglected. Therefore, the original raw opto-electronic conversion factors (OECFs) in the apparatus will lead to a distortion of the original image and result in image quality problems including chromatic aberration, color temperature error, low contrast, shift in the gray scale or unstable skin tone color.
In brief, because the conventional imaging apparatus often disregards the opto-electronic characteristics of the apparatus itself, the output image is often distorted and has a poor display quality. Furthermore, the conventional method merely uses software and complicated color reproduction techniques to adjust the quality of images. Thus, the present invention proposes a method for calibrating the deviation of opto-electronic characteristics and apparatus thereof so that the opto-electronic characteristics of the imaging apparatus are suitably considered. Ultimately, image distortion is minimized and a better control of the image quality is obtained.